The effect of alpha-lipoic acid on temporary threshold shift in humans: a preliminary study

Noise-induced hearing loss (NHIL) is a significant source of hearing loss in industrialized countries. Recent research on the cellular bases of NIHL has led to new avenues for protection through prophylactic drugs. Although in experimental animal models several compounds have shown a protective effect in NIHL, limited data are available in humans. Many authors are focusing their attention on the role of antioxidant on hearing protection. Alpha-lipoic acid (ALA), an essential cofactor in mitochondrial enzymes, is a novel biological antioxidant and a potent free radical scavenger and, in animal models, it has been shown to protect from age-induced and cisplatin-induced hearing loss. The aim of our study was to evaluate the effect of alpha-lipoic acid on temporary threshold shift measured 2 minutes after the end of exposure (TTS(2)) induced by a 3 kHz tone in young normally hearing subjects. Thirty young normal hearing volunteers served as control subjects. Individuals were randomly assigned to three groups. Group A (10 subjects) subjects were exposed to a 90 dB HL 3 kHz pure tone for 10 min. Group B (10 subjects) subjects were exposed to a 90 dB HL 3 kHz pure tone one hour after oral ingestion of 600 mg of ALA. Group C (10 subjects) were exposed to a 90 dB HL 3 kHz pure tone after 10 days of oral ingestion of 600 mg of ALA. Statistical analysis showed that prior to the exposure the hearing thresholds did not differ significantly among the three groups. TTS(2) of group C was significantly lower that TTS2 of Groups A and B at 6 kHz (p 0.03), and TEOAEs amplitude change after noise exposure was lower for group C compared to Groups A (p = 0.089) and B (p = 0.03). ALA is a powerful lipophilic antioxidant and free radical scavenger currently used in clinical practice. A single dose of 600 mg of dose ALA did not induce any protection on the TTS(2) induced by a 90 dB HL 3 kHz tone, while 10 days of therapeutic dosage assumption of ALA was associated with significant protection at 6 kHz. The results of this study show that a short course of ALA protects from TTS(2) in humans, and therefore further studies are needed to better define the role of ALA in the prevention of noise induced hearing loss.